Abstract
Purpose: :
To investigate the relationships between changes in the aqueous outflow facility (C), hydrodynamic outflow patterns and morphology following acute intraocular pressure (IOP) variation in bovine eyes using a two-color tracer technique to label two outflow patterns within the same eye.
Methods: :
Twelve fresh enucleated bovine eyes were perfused with Dulbecco's PBS(DPBS) containing 5.5 mM glucose at 30 mmHg first to establish the baseline C followed by a fixed volume of red fluorescent microspheres (0.5µm, 0.002% v/v). After the anterior chamber was exchanged with DPBS to remove the red tracer, perfusion was continued at 7 mmHg with the same volume of green tracer, followed by a fixative. To estimate the washout effect 2 control groups were included in which the eyes were constantly perfused at either 30 (n=6) or 7 mmHg (n=6) using the same methods. The C was continuously recorded. Confocal images were taken along the inner wall (IW) of the aqueous plexus (AP) in frontal sections. The percent of the effective filtration length (PEFL = IW length exhibiting tracer labeling/total length of IW) was measured. Sections with AP were processed and examined by light microscopy. The total length of IW and the length exhibiting separation (SL) in the juxtacanalicular tissue (JCT) were measured. A minimum of 8 collector channel (CC) ostia per eye were analyzed for herniations.
Results: :
In the experimental (30-7mmHg) group, the C was significantly higher at 7 mmHg (4.81±1.33µl/min/mmHg, Mean ± SD) than that at 30mmHg (0.99±0.15µl/min/mmHg, p=0.002), corresponding to a significant increase in the PEFL at 7 mmHg than 30 mmHg (p=0.0003). The percent of CC ostia exhibiting herniations in the experimental group (67.40±8.90%, Mean±SE) decreased significantly than that in the control 30mmHg (94.44±3.33%, p=0.03), but higher than in control 7mmHg group (29.43±4.60%, p=0.01). Washout associated separation between the IW and JCT was found and percent of separation length was decreased in control 30mmHg compared to the experimental and control 7mmHg groups. This decrease was associated with more collapse of AP in control 30 mmHg group which limited the separation and confined it to the CC ostia region.
Conclusions: :
As the IOP was decreased from a high to a normal level, the pressure-induced morphological and hydrodynamic changes were reversible, but not to a baseline level. Our data suggest that morphological changes related to elevation of IOP and washout (collapse of AP, separation between the JCT and IW, and herniation into CC ostia) influence the effective filtration area that regulates C.
Keywords: outflow: trabecular meshwork • intraocular pressure • trabecular meshwork